A navigation system performs travel guidance for enabling a user to easily and quickly reach the selected destination. A typical example is a vehicle navigation system where a vehicle carries a navigation function. Such a navigation system detects the position of the user or user's vehicle, and reads out map data pertaining to an area at the current vehicle position from a data storage medium in the navigation system. The navigation system displays a map image on a monitor screen while superimposing a mark representing the current location of the user on the map image. When a destination is set, the navigation system starts a route guidance function for setting a guided route from the start point to the destination and guides the user to the destination.
FIGS. 1A-1H show an example of overall procedure and screen display involved in the navigation system. FIG. 1A shows an example of locator map screen of the navigation system typically used when the destination is not specified. The navigation system displays a street on which the vehicle (current vehicle position VP) is running on a map image and a name of the street. Other information such as a north pointer NP, a map scale and a current time may also be illustrated on the display screen.
FIGS. 1B-1F show an example of process for specifying a destination in the navigation system. When selecting a “Destination” menu on a main menu screen of FIG. 1B, the navigation system displays an “Find Destination By” screen as shown in FIG. 1C for specifying an input method for selecting the destination. The “Find Destination By” screen lists various methods for selecting the destination. This example includes the methods of “Address”, “Intersection”, “Point of Interest”, “Recent Route”, “Address Book”, and “Today's Plan” which are well known in the art.
When selecting, for example, the “Address” method in FIG. 1C, the navigation system displays a keyboard screen in FIG. 1D. Suppose the user inputs an address “2525 W. Carson” of a “Del Amo” shopping mall, the navigation system displays a “Confirm Destination” screen such as shown in FIG. 1E. If the name and address on the screen shows the correct destination, the user enters an “OK to Proceed” key to proceed to the next procedure.
In FIG. 1F, the navigation system calculates and determines a route to the destination, i.e., the address “2525 W. Carson”. The navigation system determines a route to the destination based on, for example, the quickest way to reach the destination, the route using many free ways as possible or the route without using toll road, and the like. In this example, the navigation system displays a progress scale of the calculation of the route.
Once the route to the destination is determined, the navigation system starts the route guidance as shown in FIG. 1G for guiding the user to the destination. Typically, the navigation system shows the intersection which is highlighted to show the next turn and a direction of the turn. Such route guidance by the navigation system is also accompanied by voice instructions. By approaching every intersection to turn, the navigation system automatically displays the intersection guidance diagram to instruct the user which direction to turn at the intersection.
The navigation system measures a distance to the current destination to detect whether the destination is within a predetermined range such as within 100 meters. When the user approaches the destination within such a predetermined distance, the navigation system indicates that the destination “Dest” is ahead as shown in FIG. 1H. The navigation system detects the actual arrival based on various factors such as the engine stop.
As noted above, a process of entering a street name (address) is frequently needed when setting a destination in the navigation system. FIG. 2A shows a display example on a screen of a navigation system for entering a street name for specifying an address of a destination. This display example is functionally equivalent to the display shown in FIG. 1D. In FIG. 2A, a keyboard 28 is used to enter a street name and street number, and a window 27 shows characters entered by a user or candidate street names based on the characters specified by the user.
In entering a street name, the user must have a sufficiently solid recollection of the desired street name and its spelling. Unless the user knows the name of the street or correct spelling of the street name, the user will not be able to set the navigation system to the desired destination. Moreover, even when the user knows of a correct spelling for a destination, inputting all the characters for the street name is cumbersome and error-prone.
To overcome the shortcomings above, an incremental matching method is proposed. This method searches candidate street names as soon as any character is input and disables keys that will not be followed by characters that have entered for the candidate street names to help the user to press correct keys. An example of a display utilizing the incremental matching method is shown in FIG. 2B. The user has input “ASHL” as the first four letters of a desired street name. Disabled keys are shadowed and cannot be entered because disabled letters will not follow the input as a valid street name. In this example, only the keys “E” and “A” are enabled because possible street names that satisfy the user's input are “ASHLAND CIR”, “ASHLAND PL”, “ASHLEAF”, “ASHLEY CT” and “ASHLEY PL”.
However, even if this method is used, the navigation system will fail to disable adequate number of keys to help the user in inputting a desired street name if the user remembers only the first few letters correctly. In the example above, the user may only remember that the desired street name starts with “ASH” and is not certain for the rest. In such a case, the navigation system may fail to narrow down the candidate street names, and accordingly, fail to disable adequate keys on the keyboard 28 to help the user. Moreover, the user may be confused by the similar sounding street names, such as “ASHLEY” and “ASHLEAF”, resulting in mistakenly selecting a wrong street name.
Thus, there is a need to provide an efficient and effective method of assisting the user to input a desired street name in a navigation system.